Graphite-based structures or devices, e.g. graphene quantum dots, graphene nanoribbons (GNRs), graphene nanonetworks, graphene plasmonics and graphene super-lattices, exhibit many exceptional chemical, mechanical, electronic and optical properties, and are very desirable for use in electronic devices, composite materials, and energy generation and storage. Such graphite-based structures in general comprise a graphene layer, typically nanometers thick and having a characteristic dimension also in nanometers range. For example, in order to obtain adequate band gaps for operation at room temperature, GNRs are required to have a width within a few nanometers due to the inverse relationship between the band gap and the width of the GNRs. Moreover, graphene layers with multiple levels, different pitch and duty cycle combinations are very desirable, which allows for the design of graphene devices with multiple functions, enhanced efficiency, and/or high packing density.
Current methods for fabricating such graphite-based structures are complicated, expensive, inefficient and highly inconsistent, and are mainly limited to laboratories. These methods can be broadly classified as epitaxial growth, chemical vapor deposition (CVD) growth, colloidal suspension, unconventional methods and exfoliation (See, e.g., Jayasen and Subbiah, 2011, Nanoscale Research Letter, 6:95; Parrish, “Graphene Growth Techniques for Use in Nanoelectronics).
Current fabrication methods generally involve patterning graphene, after graphene generation, into desired shapes and sizes. Patterning graphene, however, is very difficult because maintaining selectivity when etching carbon based materials is difficult in relation to other materials. It is in particular a notoriously difficult process in the nanoscale dimensions. As a result, current methods have several drawbacks. For example, the required etching for patterning graphene sheets into desired shapes often produce graphite-based structures with unpredictable geometries and erratic edge structures, yielding unsatisfactory functionalities of the graphene devices. Also, current methods generally use horizontal isolation, resulting in less usable surface area, lower packing density and accordingly lower efficiency of the graphene devices.
Given the above background, there is a need in the art for fabrication methods that can produce controllable, reliable and precise graphite-based structures without patterning the graphene layers, and in some cases, with multiple functionalities or high packing density.